Project Summary/Abstract In this project, two biomaterial approaches will be developed to investigate how macrophages are reprogrammed by their microenvironment and to block the undesired consequences of this reprogramming. Macrophages are capable of infiltrating solid tumors and can phagocytose cancer cells provided that inhibitory ?self?-signaling pathways are blocked and pro-phagocytic signals are present. This approach is the basis for a recent adoptive cell transfer therapy using engineered bone marrow-derived macrophages (eMDMs) to treat solid tumors. While this therapy was shown to be safe and effective at shrinking tumors in mouse models, further improvements are required for successful translation. A major barrier that must be overcome is the relatively rapid loss of the phagocytic ability of eMDMs and their acquisition of an M2-like phenotype that is similar to tumor-associated macrophages. Macrophage reprogramming by the tumor microenvironment results in increased expression of SIRP?, a cell surface receptor that recognizes the CD47 ?marker of self? protein that is overexpressed on many cancer cells. It is hypothesized here that increased SIRP? on reprogrammed macrophages sensitizes them to CD47 on cancer cells and inhibits phagocytosis. In Aim 1, polymeric nanoparticles will be used to deliver small molecule drugs and microRNAs to eMDMs in order to maintain a low SIRP?, phagocytic phenotype. Drug-loaded nanoparticles will be taken up by eMDMs prior to their injection into tumor-bearing mice. Localized, sustained release of drugs that suppress SIRP? expression is anticipated to prolong phagocytosis and to improve tumor shrinkage. In Aim 2, engineered polyacrylamide hydrogels will be used to investigate how substrate stiffness acts a physical cue to regulate self- signaling between macrophages and cancer cells through the CD47-SIRP? axis. Preliminary data suggest that SIRP? expression increases on stiff substrates, providing a potential mechanism by which stiff tumor microenvironments might reprogram macrophages and inhibit phagocytosis of cancer cells. Together, the approaches in Aims 1 and 2 demonstrate how biomaterials can be used to study and engineer biology, specifically immune cells. Successful completion of these aims will have a significant translational impact (i.e. the improvement of macrophage based therapies) and provide important new insights into cell biology and mechanobiology (i.e. an understanding of how physical cues influence self-signaling in the innate immune system). These aims are part of the Research Training Plan for my postdoctoral fellowship and provide the opportunity for me to acquire both depth by enhancing my biomaterials skill set and breadth by developing new expertise in cell biology, cancer biology, and immunology. This will position me for success in attaining my goal of becoming an independent investigator working at the interface of these disciplines.